Steven Gerrard fears Rangers will be without Scott Arfield for the rest of their crucial January run.
The midfielder sat out last weekend's Old Firm win over Celtic after damaging ankle ligaments against Hibernian on Boxing Day.
That 1-0 victory over Neil Lennon's team opened up a 19-point lead at the top but the Light Blues still have to prove they can go the distance having seen their title push blow up in each of the past two seasons.
And they now face a pivotal string of fixtures before the month is out which could go a long way to deciding their Premiership fate, starting with Sunday's trip to Aberdeen.
They then face visits to Fir Park and Easter Road either side of their Ibrox showdown with Ross County but will have to cope without key man Arfield as Gerrard confirmed he is unlikely to return in January.
"Scott's about to come out of a boot that he's been in since the injury," said the Rangers boss.
"He's got quite a significant injury. He's progressing well but in the short term Scott will be missing. It is difficult to put a date on Scott.
"What I would say is that knowing Scott, and if he keeps progressing as he has, you are looking at probably the end of the month all being well.
"It's an injury that you can't really rush and push, as much as you want to. So we are probably looking at four to five weeks for this type of injury.
"He has been out for a couple already so you are looking at probably the end of January, the beginning of February. We will look to see how that plays out."
To make matters worse, Kemar Roofe will also be absent for this weekend's Dons clash after lasting just 45 minutes against Celtic before a quad injury forced him off.
But Gerrard has better news on Ryan Jack's progress as the midfielder looks to make his comeback after more than a month out with a persistent knee problem.
He said: "Kemar won't be with us at the weekend. It's difficult to put a date on that one just yet but I predict he could miss a couple of games.
"There's better news on Ryan Jack, who has been outside and had two or three sessions and is progressing extremely well.
"If that keeps moving in that direction he should be back with the team sometime in the middle of next week."
Meanwhile, Gerrard confirmed he is set to trigger Rangers' option to extend Leon Balogun's one-year deal after the Nigeria international's impressive displays since moving north from Wigan back in the summer.
Derby hero Allan McGregor is also entering the final six months of his deal but Gerrard is happy to let the goalkeeper – who turns 38 at the end of the month – decide his own future.
Gerrard said: "There's no talks with any of the players at the moment but that doesn't mean that we're not keen to keep them with us.
"Allan's in fantastic form and we're really pleased with him. I think Allan's situation is a bit different than most because of his age.
"I think it will be a case of what Allan wants to do, so at the right time I'll sit down with Allan and we'll speak to the people who represent him and we'll have an open discussion on that one.
"But we're really pleased with his form. It won't be a case of judging him on his age, it will be a case of what Allan wants in terms of his own future and we'll be very respectful to that.
"Leon is someone we want to keep hold of. He knows that, he is performing ever so well.
"He signed a contract with an option of an extension on that contract and we want him to be here beyond this season.
"There is no rush in terms of that one. Leon knows he's wanted here. I think he's enjoying it, he's playing with a smile on his face. He's come in and made the team and the squad a lot stronger."
